Matrix stabilized porous burner technology is an advanced combustion method in which a mixture of fuel and oxidizer is burned within a solid porous medium, as opposed to open, burner-stabilized flames such as that on a Bunsen burner. The advantages of porous burners over that of burner-stabilized flames is mainly due to the thermal feedback effect provided by the solid medium through which heat conduction in the upstream direction results in preheating the incoming reactants. The process yields a flame temperature higher than the equilibrium adiabatic value achievable by the fuel-oxidizer mixture in the absence of a porous medium. This process is called superadiabatic combustion. The heat transfer can be further enhanced by increasing the surface area to volume ratio of the porous medium and by the increased mixing due to turbulence generated in the porous structure. Therefore porous burners help to sustain lean flames of fuel-oxidizer mixtures lower than the conventionally known lean flammability limit, and can also be used for burning low-calorific gases. Applications of porous burner technology include power generation via thermoelectric devices, small scale heating purposes, and combustion of low-calorific value landfill-seepage gases.
It is generally accepted that alumina (Al2O3) porous matrix is catalytically inert and does not participate in the enhancement of the combustion reaction inside of the porous media. Some attempts were used to investigate the effect of silicon carbide (SiC) ceramic to verify if the lean limit can be extended in the combustion inside of the SiC porous matrix. Previous work on superadiabatic combustion in Al2O3 and SiC coated porous media was devoted to the investigation of temperature and lean limits for combustion reactions and comparison of the performance of these two materials. In that work, the porous burner was built utilizing porous alumina foam with 85% of porosity, 2-3 mm average pore size, as a combustion chamber. Two honey comb alumina flame arresters were located at both sides of the porous matrix to ensure the efficient gas mixture delivery to the combustion zone, the three alumina parts were enclosed inside of the stainless steel casing and one thermoelectric module was attached to the hot surface of the steel casing that electric current can be generated and power can be harvested from the produced heat. It was established that SiC surfaces of the porous combustion matrix might be a good promoter of the combustion for the stoichiometric fuel to air ratio, which performed in a better way in comparison with inert Al2O3 surfaces. However, SiC coated porous media did not outperform the inert Al2O3 matrix when the lean mixtures were used. The microscopy analysis of the surfaces of the of the porous media within the zones where combustion occurred revealed that while the carbon deposits were formed on catalytically inert Al2O3 surfaces, there were no deposits found on the SiC coated surfaces in the case where stoichiometric mixtures were used. Thus, SiC helps to promote the complete combustion reactions, however, it is possibly prone to the oxidation itself during combustion and, once the significant amounts of SiO2 phase forms on the surface of SiC, the catalytic properties of the ceramic will degrade.
Noble metals, such as platinum (Pt) or palladium (Pd), show high methane combustion activity at low temperature, and they, indeed, are very promising candidates to promote combustion reactions. However, while catalytic activity of noble metals is high, their cost is also very high, and their possible sublimation and/or sintering can occur in a catalytic burner at high temperatures in the presence of water and CO2 gasses. Another problem in the catalytic combustion of methane and other hydrocarbons is carbon deposition and, as a result, catalyst deactivation.
Porous burner technology, as described herein above, in internal combustion engines fuels everyday machines including water heaters, gas stoves, boilers, and portable generators, along with turbine combustion chambers and more. Conventional engines have relied on complex control equipment and large devices whose configurations created undesirably large pressure drops across the combustion chambers, compromising ideal combustion efficiency while requiring intricate control systems, making them impractical for use outside of academia.
Accordingly, due to increasing levels of environmental concerns and conservation of energy resources, there is a need in the art for burning low-calorific value gases and lean mixtures. Additionally, there is a need in the art for new and more active catalysts that would be better suited to promote combustion, reduced the recirculated energy requirement needed to stabilize the flame, and facilitate the superadiabatic combustion to generate cheap and efficient heat without significant pressure drop.
Background Section Disclaimer: To the extent that specific patents/publications/experiments/work are discussed above in this Background Section or elsewhere in this application, these discussions should not be taken as an admission that the discussed patents/publications/products are prior art for patent law purposes. For example, some or all of the discussed patents/publications/experiments/work may not be sufficiently early in time, may not reflect subject matter developed early enough in time and/or may not be sufficiently enabling so as to amount to prior art for patent law purposes. To the extent that specific patents/publications/products are discussed above in this Background Section and/or throughout the application, the descriptions/disclosures of which are all hereby incorporated by reference into this document in their respective entirety(ies).